1. Field of the Invention
The present invention relates to an electron gun in a cathode ray tube for a color TV receiver or an high definition industrial monitor, and more particularly, to a focusing electrode in an electron gun which has a more powerful dynamic quadrupole lens and applicable to cathode ray tubes of similar models.
2. Discussion of the Related Art
The electron gun used in a color cathode ray tube is a device for forming a pixel by focusing three electron beams emitted from cathodes onto a fluorescent surface with red, green, and blue fluorescent materials coated on an inside surface of a screen and illuminating the fluorescent materials.
FIG. 1 illustrates a cross-sectional view of an background art in-line type electron gun, FIG. 2A illustrates a front view of the first focusing electrode shown in FIG. 1, FIG. 2B illustrates a sectional view across line I--I shown in FIG. 2A, FIG. 3A illustrates a front view of the second focusing electrode shown in FIG. 1, and FIG. 3B illustrates a sectional view across line II--II shown in FIG. 3A.
Referring to FIGS. 1 to 3B, the electron gun 1 is provided with a triode part 2 for forming electron beams and a main focusing lens part 3 for focusing the electron beams. The triode part 2 is provided with cathodes 4 for emitting thermal electron beams, a controlling electrode 5 for controlling the thermal electrons, and an accelerating electrode 6 for accelerating the thermal electrons toward the screen. The main focusing lens part 3 disposed next to the triode part 2 includes a focusing electrode 7 and an anode 8. The focusing electrode 7 is provided with a first focusing electrode 71 having vertically elongated rectangular electron beam through holes 712 on one end 711 and adapted to be applied of a low static voltage, and a second focusing electrode 72 having horizontally elongated rectangular electron beam through holes 722 on one end 721 facing the first focusing electrode 71 and adapted to be applied of a high dynamic voltage synchronous to a deflection of the electron beams. The anode 8 is disposed next to the second focusing electrode 72 and adapted to be applied of a positive voltage.
Upon application of required voltages to the electrodes, the electron beams are controlled and accelerated to a required speed by the controlling electrode 5 and the accelerating electrode 6. The electron beams then pass through the dynamic quadrupole lens generated by a voltage difference between the static voltage of the first focusing electrode 71 and the varying voltage of the second focusing electrode 72.
In the dynamic quadrupole lens, the electron beams are applied of a focusing power stronger in the horizontal direction when the electron beams pass through the vertically elongated rectangular electron beam through holes in the first focusing electrode which is involved in focusing of the electron beam as the electrode is applied of a low static voltage and applied of a diverging power stronger in the vertical direction when the electron beams pass through the horizontally elongated rectangular electron beam through holes in the second focusing electrode which is involved in diverging the electron beams as the electrode is applied of the high dynamic voltage.
Accordingly, the electron beams are elongated in vertical direction by the dynamic quadrupole lens. Then, the electron beam, elongated in the vertical direction, is converged by a main focusing static lens formed by a voltage difference between the second focusing electrode 72 and the anode 8.
Thereafter, the electron beams are finally accelerated by the positive voltage toward the screen and deflected by a non-uniform magnetic field formed by deflection yokes (not shown). The non-uniform magnetic field elongates the electron beams in the horizontal direction, thereby causing haze which is a thin dispersion of an image on upper and lower sides of a spot of the electron beams on the screen though it can correct a convergence of the electron beams. However, as explained, the electron beams are elongated in the vertical direction in advance by the dynamic quadrupole lens, the electron beams are not elongated in the horizontal direction seriously by the non-uniform magnetic field.
In the meantime, there are cases when a more powerful non-uniform magnetic field, subsequently with a more powerful dynamic quadrupole electrode, is required. However, there has been a limitation in providing a more powerful dynamic quadrupole lens only by using aspect ratios of the electron beam pass through holes in the first, and second focusing electrodes formed in respective ends of the first, and second focusing electrodes which have limits in sizes.
Further, the background art electron gun was cumbersome in designing different first, and second focusing electrodes for providing dynamic quadrupole lenses of different power for color cathode ray tubes of models not so much different in their sizes.